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Squink
2005-Oct-27, 06:08 PM
The Aerofoil Works Backwards: (http://www.physicsweb.org/articles/news/9/10/14/1)
The flow of air over the wings of an aeroplane provides the lift that keeps it in the air. However, physicists in France have discovered that when a foam flows over an aerofoil, the resulting force is exerted downwards rather than upwards. The force - which the team calls anti-inertial lift - could have implications in fields as diverse as oil extraction and industrial cleaning processes

publiusr
2005-Oct-27, 06:57 PM
The Aerofoil Works Backwards: (http://www.physicsweb.org/articles/news/9/10/14/1)

That is cool!

Some other links:

Censorship:
http://spacefellowship.com/Forum/viewtopic.php?t=1485

Nice exhibit http://www.spaceexhibit.com/

A History Of...
http://www.space.com/missionlaunches/vandenberg_051021.html

Solar Breakthrough
http://www.spacedaily.com/news/solarcell-05i.html


Rock(et) music http://www.spacedaily.com/news/rocketscience-05zzo.html
Com-System 2.0 http://www.spacedaily.com/news/dsn-05e.html

Death Ray
http://www.livescience.com/scienceoffiction/051024_death_ray.html


China Races ahead
http://www.spacedaily.com/news/china-05zzzzzzzzzzb.html
http://www.space.com/missionlaunches/051021_shenzhou6_orbital_module.html

As Does Russia
http://www.space.com/news/ap_051016_russia_spaceplan.html
http://www.spacedaily.com/news/spaceport-05m.html
http://www.spacedaily.com/news/spacetravel-05zzzx.html


New sensor http://www.spacewar.com/news/miltech-05zzzs.html
Nano-Chains http://www.spacedaily.com/news/nanotech-05zzzzl.html
Hot Wheels http://www.spacedaily.com/news/nanotech-05zzzzn.html
Solid Fury http://www.spacewar.com/news/missiles-05zzzzo.html
Space weed http://www.spacedaily.com/news/life-05zzzzzzzb.html

Punch out
http://www.space.com/scienceastronomy/051017_spitzer_andromeda.html
Pop Rocks
http://www.livescience.com/othernews/051018_popping_rocks.html

01101001
2005-Oct-27, 07:13 PM
The Aerofoil Works Backwards: (http://www.physicsweb.org/articles/news/9/10/14/1)

What's the angle of attack in the illustration (http://www.physicsweb.org/articles/news/9/10/14/1/051014)? If there was an airplane connected to that airfoil, it looks like it would be nose down. Anyone able to eyeball-estimate angle of attack?

Could they have set the airfoil to a slight negative angle of attack, so that in air it would achieve zero lift, to see what the foam effect would be in that state?

01101001
2005-Oct-27, 07:16 PM
What's the angle of attack in the illustration (http://www.physicsweb.org/articles/news/9/10/14/1/051014)? If there was an airplane connected to that airfoil, it looks like it would be nose down. Anyone able to eyeball-estimate angle of attack?

Could they have set the airfoil to a slight negative angle of attack, so that in air it would achieve zero lift, to see what the foam effect would be in that state?

And a second thought about the title of this topic: if the lift is negative in this configuration, why wouldn't the plane be able to fly -- upside down in foam?

The Mangler
2005-Oct-28, 12:06 AM
What's the angle of attack in the illustration (http://www.physicsweb.org/articles/news/9/10/14/1/051014)? If there was an airplane connected to that airfoil, it looks like it would be nose down. Anyone able to eyeball-estimate angle of attack?

As I work on/around aircraft nearly every day, I would estimate that the AoA is approx. -10deg. to -15deg. (nose down). Although, most wings don't have that drastic of a curve, it may just be a "test" airfoil. The shape of the airfoil show would be close to a wing with flaps & slats down. (usually only used for landing, flaps & slats increase lift (by increasing the surface area of the wing) allowing the plane to fly slower)

-edit-
After a second look, it looks like the slats (front) are clean (up), and the flaps are maybe 10deg. down. The whole wing still looks like it has approx. -10deg. AoA.

enginelessjohn
2005-Oct-28, 09:12 AM
It's an undercambered wing section, so the chord is calculated as a line between the forwardmost and aft most points. AoA is the angle relative to this, which would be pretty close to zero, assuming the flow is horizontally left to right.

See

http://www.grc.nasa.gov/WWW/K-12/airplane/geom.html

and

http://www.aerospaceweb.org/question/aerodynamics/q0165.shtml

Cheers
John

The Mangler
2005-Oct-28, 11:46 PM
OK. I guess what I was trying to say was that the illustration doesn't look much like an actual wing. The diagrams in your links look more realistic (more like what I'm used to seeing).

publiusr
2005-Nov-04, 07:04 PM
It's an undercambered wing section, so the chord is calculated as a line between the forwardmost and aft most points. AoA is the angle relative to this, which would be pretty close to zero, assuming the flow is horizontally left to right.

See

http://www.grc.nasa.gov/WWW/K-12/airplane/geom.html

and

http://www.aerospaceweb.org/question/aerodynamics/q0165.shtml

Cheers
John

Good to see an engineer here. I love that mantra about the glass being twice as big as it needs to be.

pappy
2005-Nov-06, 03:10 PM
On an IQ scale of 1 to 10 I would put everyone here at 10 and I would be at 1, so be gentle with me. I can't even believe I'm posting on this board as I don't understand 90% of the topics discussed, but here goes. Take a flat sheet of plywood and paint a target on it, throw a snowball at the center and the force will knock down the plywood. Place the plywood at a 45 degree angle to the ground and throw another snowball. The plywood will be forced up and back or down and back depending on if the angle is facing towards you or away from you. It's all so very simple! Here's my question, why does this all change when we start talking about airplanes? High pressure, low pressure, lift, airfoil. Billions of air molecules (snowballs) thrown at the wings, hitting the bottom because of the angle, create enough force to lift the plane. I know fast moving air will cause a low pressure, i've done the air pressure over a paper will lift the paper experiment. But were talking thousands of pounds of airplane! A near perfect vacuum (a whole lot of low pressure) cannot lift water more than 30 feet, how am I to believe low pressure can lift an airplane? Please forgive me if I sound ignorant here and I do know that airplanes fly, I just disagree as to how they fly.

The Mangler
2005-Nov-06, 10:14 PM
As long as the lifting force is greater than the weight of the plane, it will have no problem (a heavy boat floats because it displaces more water than the boat weighs). That's why all aircraft have a Max. takeoff weight, if it's too heavy it will never get airborne. I'm no aerodynamist (sp?), so this is probably over simplified. Hope it helps though.

DemonWerx
2005-Nov-07, 05:04 AM
Not that I am any higher than a 1 on your IQ scale pappy, I really do love things associated with Aerodynamics and Aeronautics...

Look into the - Bernoulli Principle. It is the principle that refers to the Air as a fluid instead of it being like snowballs being thrown at the wings of the plane, and explains why they fly.

Google is a great place to search for more info. :)

~Demon

lti
2005-Nov-07, 08:56 AM
firstly Pappy, your view of an aerofoil is probably overly simplified. It isnt simply a flat solid with an angle to deflect air down (tho this is often the design of the rotors on simple toy helicopters).

the Aerofoil shape causes air to flow faster over the top than under the bottom. In fluid dynamics when the velocity of a fluid increases, the pressure must decrease to compensate. When the velocity decreases, the pressure decreases. this is to conserve the total flow rate of the fluid.
This is why blowing over the top of a piece of paper causes it to lift. Or why blowing between two pieces of paper causes them to 'blow' together (not apart as most people would think).

It isnt just the lower pressure above the wing that causes the lift, but also the greater pressure below the wing. its the pressure difference between the top and bottom of the wing that causes lift. because pressure is force divided by area, we can work out the force generated to lift the aeroplane by multiplying the pressure difference by the area of the wing.

As long as this force upwards is greater than the weight of the aeroplane, it will undergo an acceleration upwards.

simple :P

It seems however that in a foam it isnt so simple. Im no expert in complex fluid dynamics so im just gona remain in awe over the findings.

on another note, why do americans say aerofoil, but airplane? shouldnt aeroplanes have aerofoils and airplanes have airfoils?

gwiz
2005-Nov-07, 09:59 AM
A cambered wing like the one they tested would indeed generate an upward force in air at zero angle of attack.

It's difficult to find a full explanation of why an aerofoil works, though half-baked ones abound. Even the aerospaceweb link above omits any mention of the key role of viscosity in low speed lift generation. The snowballs analogy is only true for hypersonic flow where the mean free path of the air molecules is of similar magnitude to the aerofoil chord.

pappy
2005-Nov-07, 12:24 PM
Thanks, I do understand how an airfoil works and other effects of fast moving air and how it can create a vacuum (low pressure). I question the explanation of how it works. If Bernoulli had studied the effects of snow, when tightly packed into a ball then accelerated towards a stationary object what might his observations have been? He would have included charts and diagrams of side A and side B of the target object, pressure differential of both sides of target object, density of the snow ect. From his data we could then predict how much force would be needed to change the target from it's normally upright position to a horizontal position, using the standard 2 lb compacted snow in a ball formation. To say that the snow ball knocked the target down would be over simplifying a complicated chain of events.

gwiz
2005-Nov-07, 02:38 PM
on another note, why do americans say aerofoil, but airplane? shouldnt aeroplanes have aerofoils and airplanes have airfoils?

I think Americans do say airfoil, while it's aerofoil on this side of the pond.

NEOWatcher
2005-Nov-07, 05:51 PM
It's difficult to find a full explanation of why an aerofoil works, though half-baked ones abound. Even the aerospaceweb link above omits any mention of the key role of viscosity in low speed lift generation.
I was also wondering about elasticity. If you put an airfoil between two tight rubberbands, wouldn't the chord of the wing be slightly below center?

gwiz
2005-Nov-07, 06:29 PM
I was also wondering about elasticity. If you put an airfoil between two tight rubberbands, wouldn't the chord of the wing be slightly below center?
Not sure if I know what you mean by the last bit - centre of what? If you put one rubber band round an aerofoil it will become shorter and fatter? Camber will increase?

The elasticity of the aircraft structure certainly affects the aerodynamics. Both static and dynamic structural deformations have to be taken into account in aircraft design.

NEOWatcher
2005-Nov-07, 08:56 PM
I was more thinking about the elasticity of the foam itself. If the foam/rubberband needs to travel more from tip to tail on the upper surface, then it would need to stretch more to cover the distance. Since it needs to stretch more, then it is exerting more of a pressure than the foam/rubberband on the lower side. (I'm having a hard time explaining, forgive me)

devilmech
2005-Nov-08, 02:38 AM
What's the angle of attack in the illustration (http://www.physicsweb.org/articles/news/9/10/14/1/051014)? If there was an airplane connected to that airfoil, it looks like it would be nose down. Anyone able to eyeball-estimate angle of attack?

Could they have set the airfoil to a slight negative angle of attack, so that in air it would achieve zero lift, to see what the foam effect would be in that state?

From the illustration, the AoA is ~0deg, possibly slightly negative. If there was an aircraft and it were to be nose down, the illustration would have to be rotated 90deg to the left to show that. That's most likely not a real airfoil though, looks like the illustrations in my USAF tech shool material to demonstrate theoretical concepts. I would scan some and provide pics, but unfortunately I threw everything out when I got out of the military.

As for the airfoil being set to achieve zero lift, that would necessarily mean that there would also be a zero "anti-intertial" lift.

publiusr
2005-Nov-09, 07:37 PM
This discussion is hardly esoteric--in fact, future cryobots on other worlds that may have to push through slush might benefit from what is said here.